Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 72. (Budapest 1980)
Embey-Isztin, A.: Major element patterns in Hungarian basaltic rocks: an approach to determine their tectonic settings
Discussion of the results The calculated discriminant functions (F lt F 2 , F 3 ) have been plotted one against the other in Figs. 2, 3 and 7. In the following, results obtained for the different rock associations will be discussed separately. Young alkali basalts Figure 2 testifies that projection points of the young alkali basalts fall almost invariably in the WPB (within-plate basalt) field. This is by no means surprising considering the low Si0 2 and high Ti0 2 concentrations of these rocks, so typical of WPB basalts (means and standard deviations of the major elements for the investigated rock series can be found in Table 2). In respect of major element content, the young alkali basalts are rather homogenous judging from the small values of standard deviations. The CIPW norms (Table 3) calculated from the means of major element data (Fe 3+ /Fe 2+ was arbitrary taken to be equal to 0.15) show a typical ol-ne composition and since ne > 5 per cent, the composition may be regarded as basanitic according to Ringwood's nomenclature. Alkali basalts of continents and oceanic islands could not be distinguished from each other by statistical procedures (PEARCE 1976). It seems thus that the nature of the crust does not influence the composition of alkalic basaltic liquids. The chemical features of this last one are largely dependent of two factors: the physico-chemical conditions of the partial melting (P, T, PHIO, PCOÎ) and the subsequent fractionation of the crystallizing magma. Indeed, lavas of the young alkaline basaltic series in Hungary seem to represent either primary melts, that is mantle-derived magmas that have been unmodified by crystal fractionation or by other processes, or in a lesser amount, liquids that have been modified by olivine and perhaps pyroxene fractionation. The identification of basaltic liquids as primary or derivated may be carried out by using three criteria (e.g. FREY et al. 1978). First, the occurrence of spinel lherzolite nodules in a basalt proves that the magma has ascended from <leptn=s=30 km without crystal fractionation or chemical interaction with wall-rock environments. In Hungary, most of the peridotite nodules come from basaltic tuffs, however lavas of Bondoróhegy, Badacsony (Balatonfelvidék), as well as Eresztvény and Magyarbánya (Cserhát) do contain such Fig. 2. Discriminant diagram (PEARCE 1976). Fig. 3. Discriminant diagram (PEARCE 1976) Circles: young alkali basalts; Triangles: basal- for the Mecsek volcanic rocks. Circles: „true" tic andésites; Crosses: diabases; X: gabbros; basalts; Triangles: cumulative rocks; Crosses: Dots: soda gabbros from the Valley of the trachyandesites; Lines b and c represent two River Bódva complementary differentiation trends
